You need to a lot more research, but I'm feeling nice today. This is Army -specific. In a nutshell - there's no "better". They all produce good and bad officers. If you already have, or are about to get your undergraduate degree, OCS may be your only option. The problem with OCS is the class size and frequency is dependent on the needs of the service. ROTC is the main source of officer accessions, producing about 5k a year. Next is USMA at about 1100. If the Army only needs 6100 LTs that year, guess what? There will be no OCS classes held. In this era of budget cuts and drawdowns, that's a real concern.
ROTC and USMA cadets are not required to go to basic training or OCS. They spend 2-4 years in college learning basic military skills. When they graduate and earn their commission, they go straight to BOLC, the school where they learn the basics of being a 2lt in their assigned branch.
Since non-prior service OCS attendees do not have any military experience, and didn't have that 4 years in ROTC, their timeline is different. They first attend regular enlisted basic training. Upon completion, they go to OCS. After that, they go to BOLC. If, on the other hand something happens that prevents their graduation from OCS (conduct, physical test failure, academic failure, etc.) they will serve the rest of their contract as an enlisted soldier.
As far as branching goes, it's not strictly true that OCS gets the less desirable branches, but in practicality, they are the last to choose. There are only so many slots available in each branch each year, so it stands to reason that the selection will be less by the time USMA and ROTC have branched. In addition, there are some branches that are essentially never available from OCS, such as medical or aviation. If you're looking at either of those, OCS will not help you.
If you're interested in ROTC, I suggest you speak to the ROO (recruiting officer) at your desired college. Do not speak to a regular recruiter unless you want more info on OCS. They may be reluctant to process a packet for OCS - many have never done one. Be persistent and don't let them persuade you to enlist unless that's what you actually want. It is NOT easier to go to OCS after you enlist, regardless what you may be told.
Good luck.